In the past, certain special services have been made available to telephone customers to provide them with features which render their telephone usage more convenient and more flexible. For example, these services may include automatic recall, automatic callback, and message waiting.
Automatic recall is a service for automatically establishing a connection to a previously called station in response to an abbreviated dialed code. One arrangement for providing such a service is disclosed in U.S. Pat. No. 3,493,688 (Re. No. 27,422) of M. S. Schoeffler, issued Feb. 3, 1970 and reissued July 4, 1972. The patent discloses that the called directory number is automatically written into a location of a central memory designated for the service to the exclusion of any previously written directory number. By dialing an abbreviated code, the customer can retrieve the last called directory number from the designated location. The retrieved directory number is then automatically used to establish a connection to the station defined thereby.
Automatic callback service, also referred to as automatic call retry, eliminates the effort required to reach persistently busy stations. The art has progressed to the point where commercially available equipment checks the called station to determine that it is idle before any reattempt is made to complete a connection. One such interoffice callback arrangement is disclosed in U.S. Pat. No. 4,166,929 of D. Sheinbein, issued Sept. 4, 1979. This arrangement discloses facilities for processing interoffice callback information between program-controlled call processors in call originating and terminating telephone offices. Each processor includes a register for storing the calling and called station identities in response to a dialed callback code from the calling station during the initial stages of a call. The arrangement then uses this and other stored information to complete a call between the two stations when the called station becomes idle.
Another special service, called "message waiting", indicates at a called station that a calling station has left a message. When a call is not answered by the called station, a message along with the directory number of the calling party is written into a memory location dedicated for the service in response to a predetermined code entered at the calling station. In addition, a lamp is commonly lighted at the idle called station to indicate the presence of the stored message.
The problem in providing a plurality of these types of services is that each service is offered as a separate stand-alone service. In particular, each service has separate dedicated memory to store information for providing the particular service. This information commonly includes the identity of the involved stations such as the calling and called directory numbers. As a consequence, the same pair of calling and called directory numbers may be stored in these memories as many times as there are services. Furthermore, when stored in a memory dedicated to a particular service, the called and calling directory numbers are usually not accessible for any other service.